Despite the advent of many flight navigational aids, one of the most important tools for navigation of aircraft remains visual navigation. Many of today's aircraft include various safety features such as on board radar, ground proximity warning systems, and the like that provide a pilot with added information about the airspace surrounding the aircraft. These systems are a tremendous resource to aid the pilot in obtaining a better situational awareness during flight, by allowing the pilot to further interpret what he or she is visually observing. However, there are instances where these various instruments become the pilot's only resource of information because the pilot's vision is hindered.
Visual hindrances may be due to bad weather, such as fog, snow or rain, or they may be due to the time of day, such as night, dawn or dusk. Further, some visual hindrances are due to the field of view limitations of the aircraft itself. Many aircraft cockpits have a field of view that is typically limited to a forward facing area that does not provide the pilot with adequate visualization to the sides and rear of the aircraft and also does not provide adequate vertical visualization above and below the aircraft.
Obstructed vision is an important safety concern in aircraft navigation, and there has been considerable effort devoted to providing systems that increase or enhance a pilot's view from the cockpit. Systems have been developed that include the use of one or more sensors that are located on the aircraft. The sensors are directed toward a selected field of view and provide images to a display system in the cockpit, where they are, in turn, displayed to the pilot. The sensors may be video cameras, infrared cameras, radar, lidar or the like. The systems allow the pilot to choose the types of images to view. For example, in nighttime flight or fog conditions, the pilot may opt to view images from the infrared and radar sensors, while under clear conditions, the pilot may use video camera feeds.
Enhanced vision systems generally provide fairly accurate visual images to the pilot, and thereby increase flight safety. However, there are some limitations to these systems that can cause the images provided to the pilot to either be less accurate or include anomalies that may distract the pilot's view. One issue relates to the limitations of a particular type of sensor to provide suitable imaging for a given situation. For example, in twilight conditions, a video camera will still provide a discernable visual image, but the image will be degraded in detail due to the low light or obstructed conditions. An infrared sensor will provide imaging based on heat sensing, but the image from an infrared sensor will not have the benefit of the ambient light still available at twilight. In these and other similar situations, the sensor may acquire only sparse input data from which visual images are to be constructed, and further, the sparse input data may vary randomly from frame to frame of the image. This is common, for example, with lidar sensors.